Oxygen deficiency impacts on burying habitats for lesser sandeel, Ammodytes tobianus, in the inner Danish waters

Starting in 1980s, the inner Danish waters have yearly been exposed to seasonal oxygen deficiency (hypoxia). Through spatial-temporal interpolation of monitoring data (1998-2005), we investigated oxygen deficiency impacts on suitable burying habitats for lesser sandeel (Ammodytes tobianus). Furthermore, the consequences of a predicted 4 [degrees]C temperature increase within this century were investigated. Maps of bottom oxygen deficiency (oxygen saturation [is less than or equal to][S.sub.crit] of sandeel) were overlaid on maps of sediment composition. Throughout the study period (1998-2005), about 8% of the suitable sediments were affected by oxygen deficiency during an average year and 23% in the most severe year. Regional differences underlay the interannual variations. The extent of oxygen deficiency in enclosed regions varied from 20% to 33% of the suitable seabed being affected, whereas in open-water regions oxygen deficiency problems were limited during average years. However, large areas of the open-water seabed experienced oxygen deficiency during severe years. In such years, under a 4.0 [degrees]C temperature increase scenario, the extent of oxygen deficiency on open-water suitable patches was predicted to increase from 25% to about 40%. Depuis les annees 1980, les eaux interieures du Danemark sont exposees chaque annee a une carence saisonniere en oxygene (hypoxie). En faisant des interpolations spatio-temporelles dans les donnees de surveillance (1998-2005), nous examinons les impacts de la carence en oxygene sur les habitats d'enfouissement du lancon equille (Ammodytes tobianus). Nous etudions les consequences d'un accroissement predit de temperature de 4 [degrees]C au cours du siecle actuel. Nous avons superpose des cartes de deficit d'oxygene au fond (saturation d'oxygene [is less than or equal to] [S.sub.crit] du lancon) sur des cartes de composition des sediments. Au cours de la periode d'etude (1998-2005), environ 8% des sediments appropries a l'enfouissement sont affectes par le deficit d'oxygene durant une annee moyenne et 23% durant l'annee la plus extreme. Des differences regionales sous-tendent les variations entre les annees. L'etendue du deficit d'oxygene dans les regions fermees couvre de 20% a 33% du fond de mer approprie a l'enfouissement, alors qu'en eau libre, les problemes de deficit d'oxygene sont limites durant les annees moyennes. Cependant, de grandes surfaces du fond de mer en eau libre connaissent un deficit d'oxygene durant les annees extremes. Durant ces annees-la, avec un scenario d'augmentation de la temperature de 4.0 [degrees]C, nous predisons que l'etendue du deficit d'oxygene sur les parcelles appropriees a l'enfouissement en eau libre augmentera de 25% a environ 40%. [Traduit par la Redaction]
Introduction The marine coastal zone constitutes a minor part of the world's ocean but is nonetheless highly productive and plays an important role for many fish species (Beck et al. [...]